Effect of BH4 cell concentration in quorum-quenching cell-entrapping beads on EPS fractions and biofouling control in membrane bioreactors

ABSTRACT

Diagram illustrates optimal QQ bacterium concentration in cell-entrapping beads for maximizing biofouling control in membrane bioreactors. A central graph highlights a 298% increase in operational duration at 5mg/mL BH4 concentration, emphasizing protein reduction, fouling mitigation, stable treatment performance.

Quorum quenching (QQ) with immobilized bacteria is one of the emerging biological methods to counter membrane biofouling in membrane bioreactors (MBRs). Nevertheless, the optimum concentration of QQ bacteria in immobilized media is not sufficiently understood. This study examined how the concentration of Rhodococcus sp. BH4 in cell-entrapping beads affected membrane biofouling mitigation, extracellular polymeric substance (EPS) formation, and biological treatment performance under low-flux (27 LMH) and high-flux (52 LMH) conditions. Increasing BH4 concentration improved membrane fouling mitigation up to an optimal point, beyond which no further improvement was observed with increasing concentration. The optimum concentration (5 mg cell mL−1 polymer mixture) increased the operational duration up to 298%. EPS analysis showed that significant reduction in tightly bound protein fractions (66%) was strongly correlated with mitigation of irreversible fouling. Chemical oxygen demand and ammonium removal efficiencies remained stable under all conditions, and no statistically significant differences (p > 0.05) were observed among the conditions, suggesting that QQ activity did not negatively affect biological treatment performance. These results indicate that the optimal concentration, rather than maximum concentration, of BH4 is critical for effective and sustainable biofouling control in MBR systems.